1. Field of the Invention
The present invention relates generally to optical fibers, and particularly to methods of winding optical fiber onto a spool.
2. Technical Background
Optical fiber (hereinafter xe2x80x9cfiberxe2x80x9d) produced by a drawing process must be packaged into easily transportable units. Typically this is done by winding the fiber onto a spool. The fiber may be stored on the spool as it travels between intermediate process steps of the fiber making and/or testing process or the fiber may be shipped to customers on the spool. In the fiber manufacturing facility, the fiber is unwound from the spool for testing. The fiber is also unwound by customers in the process of manufacturing optical fiber cables. Therefore, the wind quality of the fiber wound onto the spool is important and must be such that the fiber can be removed (a.k.a. paid off) from the spool without breakage or sustaining damage of any sort to the fiber.
Typically fiber is wound onto spools under constant winding tension. Winding tension refers to the tensile load in the fiber when it is wound onto a spool. This may be accomplished by moving a dancer pulley, in the fiber wind path, which maintains a constant tension upon the fiber, despite any increases or decreases in fiber length through the wind path. The pulley applies a directional force which generates tension in the fiber.
If the wind tension is low, the wind quality can be poor. Winding defects include loose wrap and dogbone. In the case of loose wrap, the fiber is not wound securely around the spool and may easily unravel from the spool and/or shift on the spool which hinders the process of paying off the fiber.
The other fiber winding defect that can occur during winding is xe2x80x9cdogbonexe2x80x9d. Dogbone occurs when the fiber starts to accumulate in excess at one or both of the flanges of the spool in comparison to the fiber wound across the face of the spool. Often this will simultaneously occur at both flanges of the spool.
On the other hand, too high a tension can cause excessive deformation of the coating layers applied to the fiber. Irreversible deformation of the fiber coating is commonly referred to as xe2x80x9cflat spots.xe2x80x9d This typically occurs when the fiber is wound under too high a tension during the fiber draw process. During winding at the fiber draw, the fiber coating may still be pliable. Pressure between layers of fiber on the spool, resulting from winding the fiber under tension can cause deformation of the coating at the point of contact between two or more fibers. If the pressure is sufficiently high, the limits of the elastic deformation of the coating are exceeded and an irreversible flat spot is formed. Winding the fiber under extremely high tension may also cause the fiber to break.
One aspect of the present invention is a method of winding fiber onto a spool. The method includes varying a target tension applied to a fiber as the fiber accumulates onto the spool such that the percent change in lateral load is greater than about xe2x88x923.4% for each change of about 0.25xe2x80x3 in pack radius. Aspects of the invention also include varying the target tension such that the change in lateral load per change in pack radius comprises an amount greater than about xe2x88x9218.0 N/m2.
An additional aspect of the invention is a method of winding optical fiber onto a spool. The method includes varying the target tension applied to the optical fiber as the fiber accumulates onto the spool, such that the target tension applied to the fiber at the end of winding fiber onto the spool is at least about 0.1% or greater than the target tension at the start of winding fiber onto the spool.
Another aspect of the invention is a method of winding optical fiber onto a spool, which includes increasing the target tension applied to the fiber as the fiber accumulates onto the spool such that the lateral load applied to the fiber is substantially constant throughout the wound fiber.
The invention results in a number of advantages. For example, by practicing the invention, the wind quality of fiber wound onto a spool is improved. Practicing the invention will also result in the prevention of permanent deformation of a coating or coatings applied to the fiber without jeopardizing wind quality. Practicing the invention further results in the advantage of increasing the useable size of the spool. An increase in useable spool size can increase yields and increase utilization. Also, the invention may be adapted to existing manufacturing equipment and be practiced as the fiber is being continually drawn and wound onto the spool.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.